Position indicator



Patented Jan. '15, 1935,

UNITED STATES VPATlfzNTf OFFICE POSITION INDICATOR.

.. Rieber, Berkeley, Calif., assignor to Frank A Bieber, Inc., San Francisco, Calif., a corporation of California t v Application November 6, 1928, Serial No. 317,555

10 Claims.

especially adapted for use with electromagneticv or radio waves.

An object of my invention is to provide a means for determining the distance to the earth .from

10 an airship.

Another object of my invention is to provide a means of geophysical exploration.

Still another object of`my invention is to provide an apparatus capable of evaluating time in- I l5 tervals of the order of one twenty-millionth of a second for the purpose of determining the distance traveled by an electromagnetic wave in such an interval.

MyV invention possesses other objects and i valuable features, some of which will be set forth in the following description of my invention which is illustrated in the drawings forming part of the specication. vIt is to be understood that I do not limit myself to the showing made by the l said description and drawings, as I may adopt varying forms of my invention within the scope of the claims.

Any discontinuity in a wave propagating medium will reect a portion of a wave striking l0 it. We may class as discontinuities an abrupt A change in medium, e. g., a change from air to water in the propagation'of sound waves; or an abrupt or gradual change in the constants involved in the propagation of the waves in a; single l5 medium, as the Kennelly-Heaviside layer in the atmosphere which reflects radio waves. The reflection depends for its completeness upon the nature of the discontinuity and the angle of in- Y cidence' of the wave.

` vention comprises the method of determining the position of a discontinuity in an electromagnetic l wave propagating medium which involves generating an electromagnetic wave in the medium and evaluating the time required for that portion of the wave reflected by the discontinuity to arrive at a known point. From another standpoint my broad invention comprises the steps of gen- 0 erating a train of waves in any wave propagating medium, followed after an interval -by a second train, and adjusting the interval between the trains so that the arrival at a given point of that portion of the rst train reflected by the discon- 5- tinuity coincides with the varrival `of an unreected Yportion of the second train; The trains lmay be of different frequencies, and their coincidence may be determined by detecting their beat frequency. The position of the disconi tinuity. is determined from ythe known interval between the trains and their known speed of propagation.

Referring to the drawings:

Figure 1 is a circuit diagram of the wave generating portion of a radio-altimeter embodying my invention.

Figure 2 is a similar diagram of the Wave detecting portion of the-radio-altimeten Figure 3 is a diagram showing the form 'of the control wave which is used to regulate the interval between the Wavetrains.

Figure 4 is a wave form diagram showingl the l received wave trains and their resultant currents.

Figure 5 is a diagram showing the wave paths where the transmitting and receiving portions of the apparatus are separately located.

An embodiment of my invention particularly adapted for use as a radio-altimeter for aircraft comprises a pair of vacuum tube oscillators which are indicated in the drawing by the general reference characters 1 and 2. Except for the fact that they operate at diierent frequencies these oscillators are similar, each including a vacuum tube 3 having an anode or plate 4, a cathode 6 and a grid 7. A battery 8 and a rheostat 9 are provided for heating the cathode. The oscillating circuit comprises a grid coil 11 and a plate coil 12 tuned by a variable condenser 13. Two by-pass condensers 14 and 16, in series, connect the plate and grid coils, and a lead 17 connects from the junction between these condensers to the cathode or filament circuit. In series' with A high alternating potential of a lower/frequency Considered from one standpoint, my broad invacuum tube oscillator of any conventional type, v

and it feeds a transformer. 22. The ends of the secondary of this transformer are connected to thegrid sides of the condensers 14. The transformer secondary has a center tap which is connected to theadjustable contact of a potentiometer 23 -bridgedacross a battery 24, the positive` end of the battery being connected to the lament circuit. The potentiometer is the only control used in taking readingsI with the device, and is preferably calibrated in distance. The operation of this portion of the apparatus is as-follows: Eachof the oscillators 1 and -2 is operative over a limited Vrange of grid potentials, e. g., from o-to 5 volts. The'oscillator 21 is operative to swing thegrids 7 thru a much wider range of potentials, say 11000 volts. Since the grids o f the two oscillators are connected in op-` posite phase 4V'relation to the control oscillator their potentials vary as is shown in Figure 3, curve 26 representing the control potential on the grid of oscillator 1, and curve 27 that of oscillator 2. To Vthese alternating control potentials is added g2 adjustable direct potential from the battery If the potentiometer is adjusted to supply -5 'volts direct potential to thegrids, it is obvious vst that oscillator 1 will operate only while the control oscillator Vpotential curve 26 is falling from 5 to 0 volts or rising from 0 to 5 volts, and that oscillator 2 will operate only while the curve 27 is varying thru'a similar range. It is further obvious that the two oscillators will come into' action in immediate succession, but not simultaneously, and will each emit a short train of waves. These wave trains, which we may designate train A from oscillator 1 and train B from oscillator 2, are represented by curves 28 and 29respectively. (See Figure 4.)

If the negative direct potential is increased slightly by adjusting the potentiometer there will be a slight interval between the wave trains, as indicated at 31, Figure 3. Should the negative directpotential be further increased, say to 700 volts, the interval between. the trains will be further increased, as shown at 32, the oscillators being operative only while the control potentialsare varying between '100 and 695 volts. The maximum interval between the wave trains is equal to one half the p eriod of the control oscillator.

Thusfif the control oscillator operates at a frequency of 16,000 cycles per second, the maximum interval between the beginning of successive trains of oscillations will be l/32.000 second. As wehave assumed 1000 as the peak voltage of the control oscillator, and shall also assume a sine wave form, the minimum interval, corresponding also to the period of the wave trains, will be the period required by the oscillator to traverse an electrical. angle equal to arc sin 5/1000, or .29". This corresponds to .29/360 1/16,000` second, or approximately 1/20,000,000 second. Assuming that oscillator 1 operates at 200,000,000v cycles, and oscillator 2 at 300,000,000 cycles, this corre- Sponds to trains of 10 and 15 waves respectively. `Owing to the sinusoidal form of the control potential wave, the length of the trains increases somewhat with the interval between the trains. The interval may also be varied by changing the frequency of the control oscillator.

An extremely high positive potential will at times be impressed upon the oscillator-grids, and this would result in excessive and possibly destructive grid current were it not for the resistors 18. A soon as a grid current starts to flow there is a potentialdrop across .these resistors which keeps the grid current and voltage within reasonable limits. l

Returning to the structure of the apparatus as shown in Fig.v 1, coil 12 oiy oscillator 1 is provided with a tap 41 to vwhich the grid 42 of an amplier tube 43 is connected thru a blocking condenser 44. The cathode 46 of the ampliiier tube is provided with the usual filament supply circuit 47 which is directly connected with the filament circuit of the tube 3, and is also connected with its own grid thru the leak 48. The plate 4901 the ampliiler is connected to a tuned circuit comprising-a coil 51 and condenser l52. Plate current is supplied to the amplier by a suitable generator 53. A radiating circuit, exempliiied by the antenna 54 and counterpoise 58 is coupled to the tuned circuit by a coil 57.

Oscillator- 2 may be provided with a similar 'assenso 'y amplier as shown, but 'it' 'is usually desirable tomake this amplier of lower power and to reduce its radiationefllciency. It is frequently advisable to enclose the transmitting equipment A in the same cabinet with the receiving equipment next to be described, and under these circumstances the amplifier and radiator apparatus for oscillator 2 may be omitted entirely, suiilcient radiation being obtained from the oscillator coils themselves.

The receiving portion of the apparatus comprises pick-up circuits which are responsive to the waves emitted by both of the oscillators 1 and 2. An antenna 71 and counterpoise '72 are connected to two circuits in parallel, the rst, consisting of the inductor 73 and the condenser '74, being tuned to wave A, and the second, consisting of the inductor 'I6 and the condenser '17, being tuned to wave B. A coil 78, coupled to both of these circuits, is connected to the iilament 79 and grid 81 of a detector tube 82, thru the grid condenser 83 and leak 84. The plate 86 of the detector feeds a tuned high frequency amplifier, comprisingthe tubes 87 and 88, and the intertube coupling circuits 89 and 90. The

output circuit of the amplifier comprises the tuned circuit 91, about which is shunted an indicator, such as the neon lamp 92. The circuits 89, 90 and 91 are all tuned'to the difference or beat frequency of waves A and B. The usual filament battery 93 and plate battery 94 supply power for the receiver.

In operation, the transmitter emits the waves A and B, represented by curves 28 and 29 of Fig. 4, successively. Neither of these waves alone can ailect the indicator 92, since the receiving ampliiier is tuned to reject these frequencies, and wave A will have traveled past the receiving angtenna'by the time wave B reaches it. If, however, the transmitter and receiver are at such a distance from a discontinuity in the wave propagatingmedium that a portion of wave A reflected by the discontinuity arrives at the re ceiver simultaneously withA wave B, the twc waves will affect the detector to produce a beat frequency component which may be represented by curve 96 -of Fig. 4. This component is accepted by the amplifier, and produces an indication in this effect. The transmitter T and receiver R are shown rather widely separated, but it is apparent `that the same eiect will occur regardless oi the distance between them. The 'waves are successively emitted by the transmitter, and,`as will be seen, the wave A has traveled past the receiver along the` line TR by the time the wave B reaches R. Another portion of the wave, which is represented in the diagram 'as A', has passed downward to the discontinuity 97 where it has been reected back to thereceiver along the path TDR to arrive simultaneously with the wave B, which sensitizes the receiver for its reception.

By manipulating the transmitter an interval may always be found such asY to produce the simultaneous arrival of the waves. Since the speed of electromagnetic waves is known, (300 million meters per second) the interval between the waves A and B may be directly evaluated in terms of distance. Thus, assuming the transmitter and receiver to be contiguous, the minlmumv interval mentioned above, 1/20,000,000 second, would correspond to a wave path of 15 meters, or a distance from the apparatus to the discontinuity er '1.5 meters (24.6 its", since the wave must traverse this distance twice. The

l` maximum interval considered above, 'or l/32,000

Owing to the nature of the control potential,.

the waves will be emitted in groups in the order ABBA, ABBA, the trains joined by the vinculum being thosel whose -beats give the desired indication. Since the B wave is much weaker than the A wave, and since the reflected wave is allways much attenuated by distance, the BA beat is so weak as to giveno distinguishable indication. There is a possible source of error vin that Y the larger distance is the correct one.

the arrival of the A train may coincide with the arrival of the second B train of the group instead of the iirst. This will give too small an apparent distance; in case of amultiple indication, In a radio-altimeter, this means that an incorrect reading is always on the side of safety. .A

In the disclosure herein given, the invention has been reduced to the simplest possible terms. It is recognized that other forms of oscillator than that shown mayv be desirable, and that it would also probably be of greatadvantage to use shield-grid tubes and 'fully shielded amplifier construction thruout. Such reiinements,

however, are well known in the art, and they are not shown here since their inclusion would 'greatly confuse both drawings and specification.

Aside from its use as a radio-altimeter, my invention is of value ingeophysical exploration, since ore bodies and oil bearing strata oiferl discontinuities which will give reflections. In this case, high power and longer. waves than those -2. The method of determining the position ofy a discontinuity in a wave propagating medium which involves the steps of generating trains of waves of different frequencies at known intervals, varying the intervals to make the arrival time at a known positionof that portion of one of the trains reflected by the discontinuityncomelde with that of an unreilected portion of the other train, and detecting the .beat frequency be- I tween said wave trains. v

s.. 'nie method er determining the pestion of a discontinuity-in a wave propagating medium which involves the steps of generating alternately trains of waves of two frequencies at known iiililiilimimimiwimi t u the poeitien er' a discontinuity in a wave propmting mediuuiiA which involves the steps of generating a relatively strong wave train, generating a weaker wave train after an interval, and varying said interval te make the arrival of the weaker train at a known position coincide with the arrival of that portion of the stronger train reflected by the discontinuity.

5. The method of determining the position of Aa discontinuity in a lwave propagating medium which involves the steps of generating a relatively strong wave train, generating a weaker wave train after an interval, varying said interval to make the arrival of the weaker train at a known position coincide with the arrival ofthat portion `of the stronger trainl reflected by the discontinuity, determining the coincidence of arrival by detecting the beat frequency between the trains,y

and determining the position of the discontinuity from the magnitude of the interval.

6. Anl apparatus for determining the position of a discontinuity in a wave propagating medium,A

said waves is indicated by their simultaneous actuation of said indicating means.

sive to the simultaneous arrival ofboth of saidfrequencies, whereby a difference in length of path of said waves is indicated by their simultaneous actuation of said indicating means.

. 7. An apparatus for determining the positionl 8. An apparatus for determining the position v erating a second train of waves, receiving circuits.

responsive to the frequencies of each of said wave trains, a detector coupled to said receiving circuits, an output eireu'it fer seid detector selectlvely responsive to the beat frequency of said waves, and an indicator operated by said output circuit. K 9. An apparatus comprising a pair of wave generating oscillators of different frequencies, a control oscillator arranged to block the operation of each of said generating oscillators during a portion of the control oscillator cycle, and means for varying the portion of said cycle during which each of said generating oscillators is operative.

'10. An apparatus for determining the position of a discontinuity in a wave propagating medium, comprising a pair of vacuum. tube oscillators for generating waves of diiferent frequencies, a con- -trol oscillator coupled to the grids of said generating oscillatorsn and operative to block each of said generating oscillators during portions c its cycle and permit their successive operation duru rival of the generated waves. 

